High strength alloy for use at elevated temperatures



United States Patent HIGH STRENGTH ALLOY FOR USE AT ELEVATED TEMPERATURES Richard R. Brady, Monroeville Borough, and Edward J. Dulis, Mount Lebanon Township, Allegheny County, 'Pa., assignors to United States Steel Corporation, a corporation of New Jersey No Drawing. Filed June 10, 1959, Ser. No. 819,211

4 Claims. (Cl. 75-126) This invention relates to alloy steel possessing high strength at high temperatures and more particularly to alloys having high creep-rupture strengths at 1100 F.

In certain industries such as steam-power generating and oil-refining, equipment is subjected to stress at temperatures of the order of 1100 F. for extended periods of time. While alloy steels suitable for such use have heretofore been made, the desired long-time (1000 hours) creep-rupture strength in excess of 40,000 p.s.i. at 1100 F. have only been obtainable by using a large proportion of expensive alloying elements or boron. In addition to the foregoing creep-rupture strength, steels for such use must possess a relatively good rupture ductility, i.e. of the order of 5 to elongation per inch and also be readily forgeable by conventional methods into plates, bars, tubes, etc. While boron is beneficial for obtaining improved elevated temperature strength, it is necessary to use such quantities that the forgeability of the steels is reduced to such extent that such steels cannot be used for most applications.

Accordingly it is an object of this invention to produce a high strength steel having good creep-rupture properties at elevated temperatures combined with good rupture ductility.

It is another object of this invention to produce a high strength steel for use at elevated temperatures which is characterized by being readily forgeable.

It is a further object to produce a steel having the foregoing with a minimum amount of alloying elements.

We have discovered that a steel possessing the foregoing properties can be produced by combining with iron and carbon, chromium, molybdenum, vanadium, columbium and either tungsten or titanium as essential ingredicuts. The composition of our invention is balanced so that the steel will transform to martensite upon air cooling from austenitizing temperatures. The molybdenum, vanadium, columbium and a metal of the group consisting of tungsten or titanium are further balanced so that tempering of the martensitic microstructure produces a steel having a 1000-hour creep-rupture strength in excess of 40,000 p.s.i. at 110 F. Along with the fore- '2 going elements, the steel contains sufficient chromium to provide good resistance to elevated temperature oxidation together with fair resistance to atmospheric corrosion. In its broadest aspects, our steel should fall within the following chemical composition limits:

Carbon 0.05 to 0.30%.- Manganese 0.25 to 0.75%.- Phosphorus 0.04% max. Sulphur 0.03% max. Silicon 0.15 to 1.0%. Chromium 1.0 to 5.0%. Nickel Up to 0.75%. Molybdenum 0.50 to 3.50%. Vanadium 0.15 to 1.0%. Tungsten 0.15 to 1.0%

or titanium 0.15 to 0.75%. Columbium 0.15 to 0.75%. Balance iron and residual amounts of other elements.

We have found that preferably the molybdenum should be maintained at about 1.0% and when the steel contains more than about 0.35% titanium, the vanadium should be maintained below about .50%. Thus in its preferred form, the steel should fall within either of the following composition ranges:

Carbon .18 to .27 Manganese .35 to .65%. Silicon .35 to .65%. Chromium 2.70 to 3.25%. Nickel max. Molybdenum .85 to 1.15%. Vanadium .25 to 35%. Columbium .35 to .65%. Tungsten .55 to .90%. or titanium .35 to .65%. Balance iron and residual amounts of other elements.

For optimum properties, the above ranges should be more restricted as follows:

A, percent B, percent Carbon .20/.25 18/.22 Manganese ele mcnts.

The composition of two steels conforming to the teach-'- ings of our invention are shown in the following Table I:

TABLE I 3. The, average room temperature properties of these. steels are shown in Table II and the creep-rupture properties at 1100 F. are shown in Table III:

Norm-The steels were austenitized for hour at 2,100 F., air-cooled to room temperature;tempered for one hour at 1,200" F; and Water quenched to room temperature.

' TABLE III Creeprupture tests resizlts for the new steel at 1100 F.

Stress, p.s.i., to Produce Rupture in- Elongation Steel in 1 Inch, Percent Y 100 hr. 1,000 hr. 10,000 hr.

1 Extrapolateddata.

2 Obtained from the specimen that ruptured after the longest exposure time at 1,100 F.

N o'rE.'Ihe steels were austenitized for 3 hour at 2,100 F., air-cooled to'room temperature; tempered forone hour at 1,200 F. and water quenchedto room temperature.

The. data presented in Tables II and III show that after tempering at 1200 F., the steel of our invention exhibits room temperature tensile strengths in the range of 166,- 000' to; 203,000 p.s.i., elongations in the range of 9 to 15 percent, and a 1000-hour creep-rupture strength in excess of 40,000 p.s.i., at1100'F. The rupture ductility of the steels after creep-rupture testing at 1100 F. are in the .range of 5 to 1 percent.

As was mentioned earlier, our steel contains either tungsten or titanium. However, when the steels contain both tungsten and titanium, they do not develop the minimum desired properties. For example, the compositions of two steels investigated that contain both tungsten and titanium are shown in Table IV, and their creep-rupture strengths at.1100 F. are shown in Table V.

TABLE IV While we.have shown and described several specific. embodiments of our invention, it will be understood that these embodiments are merely for the purpose of illustration and description and that various other forms may be devised within the scope of our invention, as defined in the appended claims.

We claim: 1

1. A steel alloy characterized by high creep-rupture properties at 1100 F., and said steel containing l Percent Carbon 0.05 to 0.30 Manganese 0.25 to"0.75 Phosphorus -s 0.04 max. Sulphur 0.03 max. Silicon 0.15 to 1.0 Chromium 1.0 to 5.0 Nickel Up to 0.75 Molybdenum 0.50 to 3.50 Vanadium 0.15 to 1.0 Columbium 0.15 to 0.75

and an element selected from the group consisting of titanium and tungsten, said element being present in an amont between 0.15 and 0.75 when said element is'titanium and between 0.15 and 1.0 when said element is tungsten. Balance iron and residual amounts of other elements. 2. A steel alloy characterized by high creep-rupture properties at 1100 F., said steel containing and an element of the group consisting of tungsten and.

titanium, said element being present in an amount between 0.35 to 0.65 when said element is titanium and between 0.55 and 0.90 when said element is tungsten.

Balance iron and residual amounts of other elements.-

Chemical. composition of the steels investigated-percent CHECK ANALYSES Steel 0 Mn P s St 1 Cr Mo V W Ti Cb A 0.25 0.50 0.032 0.020 05s 2. 0. 94 0.27 0.70 0.63 0. 5i B 0.21 0.50 0.020 0.020 0.59 2.88 1.13 0.89 0.74 0.52 ;0.49

T ABLEV 3. steel gmractierizec} by high creep-rupture proper 1es at sa stee contaimng Creep-rupture test results for the new steels 7 percent Carbon .20 to .25 s r r e ss n s. i for Elan amen Manganese .35 to .55 steel p m i hz scl ll'llcofl .35 to .55

percent mmi 100 hr. 1,000 hr} Nickel um g igj' A 41,000 35,000 25.0 Molybflenum to B 34. 000 27,000 30.0 Vanadium .73 to .87

Columbium .45 to .55

Extrapolated data. Obtained from the specimen that ruptured after the longest exposure i i to time at 1100 F. Titanium 0 NoTE.-Th'e steels were austenitlrerl or hour at 2100 F., air cooled to room temperature, tempered tor one hour at 1100 F., and water quenched-toroom temperature:

Balance iron and residual amounts of other elements.

4. A steel alloy characterized by high creep-rupture properties at 1100 F., said steel containing Percent Carbon .18 to .22 Manganese .35 to .55 Silicon .35 to .55 Chromium 2.80 to 3.20 Nickel .50 max. Molybdenum .90 to 1.10 Vanadium .19 to .28 0 Columbium .45 to .55 Tungsten 0 Titanium .45 to .55

Balance iron and residual amounts of other elements.

References Cited in the file of this patent Smith: Chromium-Molybedenum and Chromium-Molybdenum-Vanadium Steels for Power Plant and Refinery Service up to 1100 E: An Appraisal of the Litera- 5 ture. Reprint of 1956 ASME paper by Climax Molybdenum Co., New York, N.Y.

UNITED STATES PATENT OEEIEE CERTIFICATION OF CORRECTION Patent N0 2,968,549 January 17, 1961 Richard R, Brady at ale It is hereby certiified that error appears in the above numbered patent requiring correction and 'that the said Letters Patent should read as corrected below.

Column 1, line 55, for 110 F, read 1100 F.

column 3 line 410, for "1 percent" read um 10 percent column 4, line 24, for "amont" read amount line 43 for "to" read and Signed and sealed this 6th day of June 1961 (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. A STEEL ALLOY CHARACTERIZED BY HIGH CREEP-RUPTURE PROPERTIES AT 1100*F., AND SAID STEEL CONTAINING 